Shaped amplifier



Nov. 19, 1946. J. R. BOYKIN 2,411,362

SHAPED AMPL IFI ER Filed April 1, 1944 fimll LIIIF A WITNESSES:

MWM

INVENTOR John R Boykin.

ATTOR Patented Nov. 19, 1946 UNITED- STATES PATENT OFFICE SHAPEDAMPLIFIER John R. Boykin, Baltimore, Md assignor to WestinghouseElectric Corporation, East Pittsburgh, Pa., a corporation ofPennsylvania Application April 1, 1944, Serial No. 529,109

4 Claims. -(Cl. 179-171) My invention relates to electronic amplifiersand, in particular, relates to the reduction in the ripple produced inthe output current of such amplifiers by causes such as the effect ofalternating heating current for the cathode, fluctuations of cathodeemission and the like. It is particularly applicable to amplifiershaving cathodes directly heated by alternating or pulsating current of afrequency greater than that impressed from the input circuit of thetube.

For certain purposes in the electronic art, it is desirable to useelectron tubes having cathodes of what may be termed U-shape which aredirectly heated by alternating current. It is also known that suchalternating-current heating tends to produce fluctuations of the outputcircuit current which may be referred to as hum which are naturally inundesirable interference with the action of the tube when it is used, toamplify a signal input current. In the prior art, the magnitude of thishum has been greatly decreased by connecting the common terminal of thecontrol-electrode circuit and the plate circuit to a point on the heatercircuit which is at the mean value of the potential between the cathodeterminals. This connection is usually made by attaching the controlelectrode and plate circuits to the midpoint of a resistor which spansthe cathode terminals. It is also known that hum effects are produced bythe magnetic field and the potential drop along the filament between theterminals of the cathode; and that by properly proportioning themagnitude of these efiects, their resultant hum in the output circuitcan be nearly eliminated.

. However, it is frequently impracticable to make the point ofattachment to the resistor spanning the cathode terminals at its exactelectrical mid-* point, and likewise impracticable in quantityproduction to produce tubes in which the other sources of hum abovementioned are ideally reduced to zero.

In accordance with my invention, however, I have found it possible tosubstantially eliminate the residual hum eifects mentioned in thepreceding paragraphs by the circuit connections shown in the drawing andabout to be described.

One object of my invention is, accordingly, to

provide circuit connections for an electronic amplifier having a cathodefilament heated with alternating current which shall enable the tube toeificiently amplify fluctuating voltages impressed on its input circuit,while at the same time sub- 2 put circuit which otherwise would beproduced by the cathode heating current.

Another object of my invention is to provide a circuit for an electronicamplifier tube which shall make it possible to effectively amplifyfluctuating currents impressed upon its input circuit while at the sametime substantially eliminating fluctuations in its output circuit due tofluctuations f electron emissivity of its cathode.

Still another object of my invention is to provide a circuit forelectronic amplifier tubes having cathode filaments directly heated byalternating current of a frequency greater than the voltage fluctuationsimpressed on their input circuits and which shall amplify thelast-mentioned voltage fluctuations, while at the same timesubstantially eliminating the hum in their output currents which wouldnormally be caused by their cathode heating currents.

Other objects of my invention will become apparent upon reading thefollowing description, taken in connection with the single figure ofdrawing which illustrates a three-electrode electronic amplifier tubeconnected up with a circuit embodying the principles of my invention.

Referring in detail to the drawing, an electronic amplifier tube l,which may be of the highvacuum type and is shown here as embodying ananode 2, a control electrode 3 and a cathode 4, comprising a U-shapedelectron-emissive filament 4 is supplied with alternating heatingcurrent from an alternating current source 5. To take one example, thefrequency of the source 5 may be 800 cycles per second. The terminals ofthe filament 4 immediately outside the tube l are spanned by a resistor6 having a tap I positioned as closely as possible to its electricalmidpoint.

An input transformer 8 impresses a fluctuating:

signal voltage which may, for example, have a frequency of 150cycles'per second in the control electrode 3 by means of its secondarywinding 9, one terminal of which is connected to the control electrode 3and its other terminal connected through a bias battery I l to theabove-mentioned tap 1.

The flow of the alternating heating current through the cathode 4 willalternately make the stantially eliminating the hum efiects in itsoutrespective end terminals thereof positive and The anode 2 isconnected through a 're-Q sistor l2 to the positive terminal of avoltage tween them; If the tap point 1 is exactly at the electricalmidpoint between the terminals of the cathode it, it will likewiseremain at the same fixed potentiala's the midpoint of the cathodeitself, and under such circumstances, no voltage having the frequency ofthe supply 5 is effectively 7 .I impressed between either the controlelectrode 3 or the anode 2 and the cathode 4. However, if

the tap point I is displaced from the electrical midpoint of theresistor 6, a-voltage having. the

frequency of the supply 5 can be shown to be an anode, at least onecontrol electrode and an impressed between both the control electrode 3and the anode 2 and cathode 4. This will result in the production in theoutput resistor '12 of a current having the frequency of the source 5.

.In acco da wi h my nvention I conne t. a capac t 1 een the. epnt p letrode 3. a he e e e This. ffec ma e he. tube, 1 actl s rea tance t be.and in er eses between he. qn q 1? ra 3 and the c hode. 4 an efie ti e cpa t nce. which equa to ILC, where C is t e. a acit c of he capa i r i5,a d P! s he. v lta e am ification o the. e ectro tube. I The i duetancof e se ondary i in t. is reierably tuned. wit t is ect ve apa itan ereso e. at he f equ ncy impressed by th ensi m r 8.; e.- t e. presentexampl i un d. to. e onate t .50 ycles.

Under such ci cumstances, the. secondary nd-- t and th apac t r i canbeshown to on.- itutea ow-pass. fi t r of theL type. for c r ents. havne he f uency of the supply source. 5,, and wra s higher arm ics therof. Because Of the resonance to the frequency supplied through e. trensirmer 8, the v ta e. fluctua ions that frequency of the control electrode3 relative Q ClQ. cat ode 4.- approximate a maximum. The mpedance o tsee ndary winding e t currents of the frequency of the. supply source.5. is, how.-

ever, uch lar er than he'efiectiveim e e of; the capacitor [5, so thatthesecondarv windnnfiiatts n. effect, to. chok the flow. of h at n resipcur e t thrqueh the c itor lined th c s, ike. a QWrimDBQfiI s u t. by-.

' esti .vqltae sp that e uen y r m. t e p between ee t plelett qde 3 enhe ca hodet. ent nd r. uch c rc mstance that t i ed he. ee e lter and;nduc anc of: w ndi 9;,- wil t ee a eve mere efiett re len -pa s filtererre e eler er hen hpseqt he eetme some. 5, 814th, or. e m le, e seedharmonic thereof which may be due to magnetic e'ifcts of. the cat deheating current and to. voltage drop." along the cathode 4, between itste m a s h e r lr s a em n a feet. be". madethatthewindIngQQand thecapacitor l5 wiutenu. tjoichoke out. from t output circuit of em ee; 4.,

. c ntr ermite tube I, such, for example, 'asjthose due to. randomfluctuations in electron em ssion? from" the The arrangement of thecapacitor l5 and the secondary winding 9 may be considered to constitutean inverse feed-back from the plate circuit to the grid circuit whichtends to increase the stability and'decrease distortion in the amplifierI. This inverse feed-back will, in fact, tend to reduce the effect ofdisturbances in the plate circuit of the tube I.

' In accordancewith the provisions of the patent statutes, I havedescribed a particular embodiment of the principles of my invention, butthese principles are obviously of broader application in ways which willbe evident to those skilled in the art. 7

- I claim as .my invention:

1. In combination with an electron tube having electron-emissivecathode, an inductive winding connectdbetween said control electrode andsaid at the frequency of input voltages impressed on said winding with ntimes the capacitance of said capacitor, where n is the voltageamplification of said tube.

2. In combination with an electron tubehaving an anode, at least onecontrol electrode and an electron-emissive cathode, a circuit forheating said cathode from a source of periodic current, an inductivewinding cojn i ected between .said control electrode and a point on saidcircuit, an output circuit connected between said anode and thelast-mentioned point, and a capacitor connected between said, controlelectrode and said anode.

3. In combination with an electron tube having an'anode, at least onecontrol electrode and a cathode heated by periodic current of apredetermined frequency, an inductive winding connected between saidcontrol electrode and saidcathode,.means for impressing on said windingaperiodic voltage which has a frequency lower than said predeterminedfrequency, an output circuit connecting saidanode to said cathode, and acapacitor connected between saidcontrol electrode and said anode;

4. Incombination with an electron tu-be'having an. anode, at least onecontrol electrode and a cathode heated by periodic current of apredetermined: frequency, aninductive winding connected between. said.control. electrode and-said cathode, means for impressing on saidwinding a periodic voltage which has a frequency lower resonate at;saidlower frequency with. timesthe capacitance of;- said capacitor,where. ,c .is. the

voltage. amplif cation. of, said tube.

JOHN- Rt BdSYKIN:

